Retrogressive tap switching during acceleration control of traction motor



Patented Oct. 12, 1954 UNITED STATES "PA'EKENT QFFICE.

RETROGRESSIVE TAP SWITCHING DURING ACCELERATION CONTROL OF TRACTION MGTUR Fennsylvania Application August 9, 1952, Serial No. 303,476

18 Claims.

Our invention relates to control-equipment which is particularly adapted for electric locomotives or other self-propelled railway-vehicles operating on a single-phase source of supply. While our invention, in its broader aspects, is probably susceptible of broader applications or uses, it was primarily designed for the control of the shunted-field operation of a series commutator-type motor, in which a large reduction in field-strength is produced by connectin a field-shunting impedance across the main series exciting-field winding of the motor, all in one step, and the shock of this step, and the possibility of flashing of the traction motor, are avoided by stepping back on the tapped voltage of the main transformer when the field-shunting step is taken. Thereafter, the full transformer voltage may be restored, in two or more steps, thus making use of the tap-switches for producing three or more steps of short-field operation, without requiring special field-shunting switches for changing the impedance of the field shunt.

The particular object of our present invention is to retrogress sequentially, while decreasing the motor-voltage when the field-shunting switching-operation is applied, using the Wellknown preventive coil for this purpose, in combination with the usual tap-switches, for preventing a momentary open-circuiting of the power-supply to the motor, in the process of changing taps on the main transformer when the fieldshunting step is made.

While our invention is thus broadly defined, not being limited to the use of individual tapswitches with interlocked sequential progression, as distinguished from drum or cam-switch types of tap-switches, particular problems and culties are encountered in applying our invention to the individual sequential-switch type of control, and an important feature of our invention relates to a means for making this sort of application.

Our invention was also primarily designed for controlling the operation of a series direct-sun rent traction-motor or motors, operating from a single-phase trolley-wire through rectifiers carried by the locomotive. As we at present analyze our invention, however, it is applicable as well to the case of series single-phase tractiommotors which are operated froma single-phase trolley wire without rectifiers.

With the foregoing and other objects in view, our invention consists in the circuits, systems, apparatus, combinations, parts, and methods of design and control, as hereinafter described, and

5:2 as illustrated in the accompanying drawing in which:

Figure 1 is a diagrammatic view of circuits and apparatus of a very much simplified, and somewhat idealized, control-equipment which involves our invention in an illustrative application or form of embodiment, omitting numerous safeguards and refinements which make up a modern railway-control installation, and

Figs. 2 and 3 are sequence-charts oi the switching-operations which are performed in the transition from the full-voltage full-field operation to the reduced-voltage shunt-field operation, and vice versa, respectively.

The control-equipment which we have illustrated in Fig. 1 is shown applied to a locomotive or other railway-vehicle, which is represented as comprising a current-collector shoe or pantograph 2! which receives power by making a sliding contact with a single-phase third-rail or trolley-wire 22. The collector-shoe 2i energizes a main step-down transformer 23 on the locomotive, and this transformer is provided with a multi-tapped secondary-winding 24, having a plurality of voltage-changing taps, such as Tl, T3 TH and TI3, at successive points along at least one portion of the secondary winding 24, such as the portion of said secondary winding between a mid-point or tap X and the highvoltage or terminal-tap Tl3.

As has been previously known, the voltage changing taps TI to T13 of the main transformer are connected to a plurality of tap-switches, such as C! to GM, for changing the taps in a pin rality of successive stages. In the particular control-equipment illustrated, and in accordance with a known preferred usage, two of these tapswitches are connected to each of the voltagechanging taps. Thus, the tap-switches Cl and C2 are both connected to the '1! tap, the tap switches C3 and C4 are both connected to the T3 tap, etc. These tap-switches CI to CM, which are used to progressively change the voltage which. is delivered by a portion of the transformer secondary winding 26, are also connected to the terminals of a mid-tapped preventive autotransformer-coil PC, in such a manner that one pre ventive-coil terminal 25 is connected to alternate tap-switches, such as the even-numbered tap-- switches C2, C4 Cl2 and CM, that is, to one of the two tap-switches for each of the voltagechanging taps of the main transformer. The other terminal 26 of the preventive coil PC is connected to the remaining tap-switches of this group of tap-switches, namely, to the odd-numbered tap-switches CI, C3 CH and CI3.

The preventive coil PC has a motor-energizing mid-tap lead 2'! which is used to apply a variable voltage to one terminal of a series commutatortype traction-motor which is shown as comprising an armature A, a serially connected interpolewindin 28, a series main-field or exciting-field winding 29, and a field-controlling re-verserswitch 39. The other terminal of the tractionmotor armature A is energized from some portion of the transformer secondary-winding 24, such as the tap or connection X, and in the particular circuit which is illustrated in Fig. 1, this motorconnection is made through a choke-coil 3I.

In accordance with the broadly stated principles of our invention, the traction motor A is provided with a control-means or motor-switching means, for making such a change in the motor-operating connections, after the maximum transformer-voltage has been applied. to themotor, in the initial stages of the motor-acceleration control, that it is necessary, at the same-time, to step back two or more steps, in the motorvoltage, in order to prevent undesirably large current-surges in the motor. In the particular form of embodiment of our invention, which is illustrated in Fig. 1, this motor-switching step consists in a field-shunting step, in which the main exciting-field winding 29 is shunted, all at once, by a field-shunt 34. As shown, this fieldshunting step is accomplished by the closure of the contact 35 of a field-shunt contactor CF.

The control-equipment includes one or more master-controllers MC, or other controlling-means which is under the control of the engineman or other attendant in charge of the control-equipment. The controller MC is illustrated as a simple drum-controller, having an off-position and seventeen running-positions, numbered 1 to 17, for connecting the desired control-circuit fingers F! to FIT in the desired sequential order. It is to be understood, of course, that the illustrated master-controller MC may be any kind. or. type of controller-means which is capable of per.- iorming the desired sequential control-functions, according to whatever order or sequential law may be desired, in any case. This master-controller MC is used, either directly or indirectly, to control the various tap-switches CI to- CIA and the fieldshunt switch-contact 35 or CF.

It is to be understood, in the broader concepts of our invention, that the main switching-contacts of our tap-switches CI to CM, as well as the main switching-contact 35 of our field-shunt switching-means CF, may have their predetermined sequential law of operation controlled in any known or desired manner. For example, these main switching contacts may for example be camswitches controlled or operated by a drum of their own (not shown), or, as shown on the drawing, they may be separate or individual electrically controlled contactors or relays, using these terms to include any contact-making devices of the broad descriptions which are given, regardless of any special restricted uses of these terms, which may sometimes be adopted in the art. We wish it to be definitely understood, therefore, in the more general aspects of our invention, that the particular switches and switchcontacts which are shown are representative of any equivalent types of switches or switch-contacts, known to the art.

In the illustrated form of embodiment of our invention, in which our present improvements are especially applicable or significant, the main switch-contacts 36 of the tap-switches CI to CM are carried by separate, electrically controlled tap-switches or contactors, all parts of which bear the same designations as the contacts, namely CI to CIZ. In like manner, the mainswitchingcontact (55 of the field-shunting switching-means CF is also carried by a separate, electrically controlled contactor.

In Our illustrated control-equipment, the first fourteen master-controller contact-fingers FI to PM are used to energize correspondingly numbered auxiliary relays XI to XM, which are in turn used to control the respective tap-switch contactors CI to CM. The master-controller finger FIE is used to control an auxiliary transition-relay XT, which will be subsequently described. The master-controller finger PI 6 is connected to a control-circuit bus The mastercontroller finger FIT is used to control the fieldshunt ccntactor CF.

In every case, each of the relays or contactors isshown in its deenergized position. Each relay or contactor is represented as havin an. operating-winding, coil, or solenoid 38 which is represented as if it were capable of lifting upon an armatiu'e-core which is represented as a small circle 39 inside of the. coil-circle 38, the referencecharacter or designations of each of the respective relays or contactors-being applied to all of its parts, by way of identification. The auxiliary relays XI to Kid and KT are light-weight, lightduty, and fast-moving relays which operate relatively quickly.

The various contactors C I. to C I 4 and CF, which carry the heavy-duty or heavy-current main-circuit contacts, are much more massive and much slower-operating switching-devices, their slower. operating-time beingv diagrammatically indicated, in the drawing, by means. of a short-circuited coil or slug 4-5, which is diagrammatically shown as a larger circle, surrounding the circle which represents the controlling-coil 38. This slug 40 is intended to represent any kind of means for producing a relatively slow action, either by reason of the large inertia of heavy parts, or by way of opening a magnet-valve (not shown), for initiating the operation of an airengine (not shown), all of which takes a certain amount of time. As far as our present invention is concerned, the important (but not essential) feature is that the individual contactors CI' to CM and CF shall make a relatively sluggish or delayed. response, when their respective operating-coils 38 are electrically energized.

In order to prevent backstair circuits, par ticularly in multiple-unit railway-trains which use train-line wires (not shown) the leads which are connected to the first fourteen master-controller fingers F! to FM; and thence to the operating-coils of the relays XI to Xll, contain unidirectionally conducting rectifiers 43, one recti fier for each circuit. The relays XI to XI are fast sequence-controlling relays, each having a contactor-controllirrg make-contact 44, which is connected in series with the coil of the correspondingly numberedcontactor CI- to GM, as the case may be. In addition, all. of the auxiliary sequence-relays XI. to XM, except the lasttwo, are provided with auxiliary circuit-breaking or backcontacts or out-interlocks 45-, and these auxiliary contacts 45 are connected, chain-fashion, to the operating-coils of the auxiliary relay having a number two numbers higher up, and so on to the remainin higher-numbered auxiliary relays, in a known manner, and as shown in Fig. l.

The tap-switch contactors CI to CM also have sequence-insuring circuit-breaking or back-contacts or out interlocks 17, which are connected in series with the operating-coils of other tapswitches, in such a manner that each tap-switch operating-coil 58 will be deenergized in response to a closed or actuated condition of either one of the next adjacent higher and lower-voltage tapswitches on the same terminal of the preventive coil PC. These tap-switch sequence-interlocks t! are also connected chain-fashion, in a manner known in the art, so that the negative side of each tap-switch operating-coil is in series with the switch-out interlock ll of the contactor having a number two numbers higher, and in series with all still-higher-numbered contactor-interlocks Ml, while the positive sides of each tapswitch coil are in series with the tap-switch interlock 47 of the contactor having a number two numbers lower, and in series with the correspond-- ing interlocks t? of all still-loWer-numbered contactors. This interlock-arrangement operates, in

tact it), until all of the other odd-numbered tapswitches are open (that is, have their main contacts open); and no even-numbered tapswitch can close until all of the other even-numbered tap-switches are open.

The operation of the tap-switch controls which have just been described is such that, at each running-step of the voltage-increasin part of the motor-accelerating means or master-controller MC, both terminals of the preventive coil PC are energized. In other words, the tapswitches CI to CM are sequentially closed in pairs, in each of the running-steps of the control, and the voltage is progressively increased by stepping up the voltage, first on one preventive-coil terminal 28 (for example), and then on the other preventive coil-terminal 25 (for example). In each case, the transitions between successive voltage-steps are accomplished by first opening the tap-switch which has been energizing the preventive-coil terminal whose voltage is to be changed, and then immediately closing the tapswitch which applies the altered voltage to that terminal of the preventive coil.

In the particular system which is shown in Fig. 1, the above-described voltage-changes are progressively made by the master-controller MC, in its positions 2 to i l, during which the several auxiliary relays Xi to Ki l are used to energize the correspondingly numbered tap-switches Ci to CM in pairs, starting with Cl and C?! on step 2, then C2 and G3 on step 3;, and so on, until the highestwoltage step M is reached, on the mastercontroller M0, at which time the auxiliary switches ms and Ki i and the two highest-voltage tap-switches C53 and Gi l are closed or energized, thus connecting both of the preventivecoil terminals Eli and iii} to the highest-voltage transformer tap T l 3.

In the particular control-equipment which is shown in Fig. I, an extra control point, or master-controller step No. 1, is provided, in order to obtain a gentle starting without requiring an extra-low voltage transformer-tap, this gentlestarting step being obtained by also energizing the master-controller finger Fl l, which energizes the field-shunt contactor CF, thus causing the motor A to start on short field, that is, with its main field-winding 2S; weakened by having the field-shunt 34 connected thereacross.

On position 14 of the master-controller MC,

6 the motor is operating on full-voltage and fullfield.

If still higher motor-speeds are desired, the master-controller is moved from step 14 to step 15, which introduces the short-field operation by energizing the contact-finger Fl! and the field-shunt contactor CF. In practicing our invention, the entire field-weakening effect of the field-shunt 34 is obtained all at once, thus avoiding the necessity for using extra field-shunting switches for weakening the field in three difierent steps or stages. In order to prevent the heavy current-rush which would occur, in the motor A, if this severe field-shunting step should be taken all at once on the full-voltage tapswitch connections, it is necessary, in accordance with our invention, to quickly and automatically reduce the applied voltage by two or more voltage steps, at about the same time when the motor-field is weakened. We say, about the same time, because a precisely nice timing is not at all necessary, because of the rather long tim constant of the motor, which makes it impossible to very quickly change the motor-flux. There is an appreciable time, therefore, during which the reduced-voltage adjustments can be made, in practicing our invention, and very good results have been obtained in a control-equipment in which the reduced-voltage connections for the short-field operation are obtained in a time which is of the order of of a second, this figure being given onl by way of example.

It is necessary, in making the adjustments to the reduced-voltage connections just described, that this shall be done without a power-interruption to the motor, as such an interruption would not only produce an objectionable loss of motoreffort for a moment, but it would also produce conditions tending to cause severe sparking at the commutator of the motor when the power is reapplied. In the broader concepts of our invent-ion, we contemplate the use of any retrogressive voltage-reduction, from the maximumvoltage condition to a reduced-voltage condition which is at least two voltage-points lower than the maximum, at the time of connecting in the field-shunt 34.

In a more particular sense, our invention relates to the accomplishment of these results in a control-equipment which uses individual or separate electrically controlled, tap-switches or contactors Cl to C52. Since the voltage-reduction is at least two steps down from the highestvoltage connection (we have shown two steps), it is necessary, in reaching this reduced-voltage condition, when the master controller MC is moved from step 14 to step 15, to simultaneously deenergize both of the auxiliary relays X53 and XM which correspond to the two high-voltage tap-switches Old and CM, and to simultaneously energize the contact-fingers FM and F12 which extend to thenext two lower-numbered auxiliary relays Xi! and XIZ, corresponding to the two tap-switches CH and CH which are connected to the next-lower-voltage tap TH on the main transformer. If the old conventional control-interlocks had been used, as thus far described alone, this would have entailed a momentary power-interruption to a motor A, and this should not be permitted.

In accordance with our present invention, therefore, we provide two auxiliary control-circuits 5i and 52, which are shown in Fig. 1 in heavy lines, inside of a dotted-line rectangle 53 which indicates the new part of our circuitdiagram. The auxiliary control-circuit is connected around the control-contact X|3 of the auxiliary relay X13, which controls the tapswitch C13, said tap-switch C13 being one of the two highest-voltage tap-switches C13 and CM, the CH tap-switch being connected to the preventive-coil terminal 26. This auxiliary control-circuit 51 includes three interlock-contacts in series; namely a CH back-contact 54, which is closed only so long as the tap-switch CIZ which is connected to the other preventive-coil terminal 25 is open or deenergized; an XT makecontact 55, which is closed when the auxiliary transition-relay XT is energized; and 21- (H3 make-contact 55, which is closed if the tapswitch ClI-l, which is being controlled, is closed at the time when the auxiliary transition-relay XT is energized. In accordance with our invention, the auxiliary transition-relay XT is energized from the contact-finger F of the master-controller MC, when the master-controller is in either one of its positions 14 or 15, and at no other time.

The result of the auxiliary control-circuit 5! is therefore that when the master-controller is moved. from its position 14 to its position 15 thereby deenergizing the auxiliary relay X13 and opening the Xl3 control-contact, this auxiliary control-circuit 5i by-passes this contact and maintains an intact circuit for the operatingcoil of the tap-switch C13, thus holding this tap-switch ClS closed until the closure of the next lower-voltage tap-switch C12, which is connected to the other terminal of the preventive coil PC.

The total switch-sequence which is accomplished by th auxiliary control-circuit 51, when the master-controller MC is moved from its notch or position 14 to its notch or position 15, is indicated in Fig. 2. As soon as the master-controller is moved to the notch or step 15, the CM tap-switch is deenergized, and drops out in due course, while the field-shunting contactor CF is energized, and closes within whatever operatingtime is built into this contactor. At the same time, the auxiliary relays XI! and X12 are energized by the master-controller, thus closing their main make-contacts 44 which are in series with the operating-coils CH and C12 respectively. As soon as the tap switch (Fl-4 reaches its open position, the CIZ coil is thus energized, causing the CIE tap-switch to close, in the step marked i513 in Fig. 2. When the tap-switch Cl2 closes, it opens its back-contact 54 in our auxiliary control-circuit 5|, thereby deenergizing the tap-switch Cl3, whereupon said tap-switch C13 opens, as indicated by the step 150 in Fig. 2. As soon as the tap-switch Cl3 opens, its top backcontact C13 completes the circuit for the C! l coil, thus causing the tap-switch CI 1 to close, as indicated by the step ISD in Fig. 2. In this manner, a step-by-step voltage-reduction is automatically made, in passing from the full-voltage full-field notch 14 to the reduced-voltage short-field notch l5, and this voltage-reduction is efiected without causing any power-interruption.

Our other auxiliary control-circuit 52 is connected around the control-contact XIZ which is in series with the operating-coil for the tapswitch CIZ, which is one of the two lower-voltage tap-switches CH and CH, having a voltage next below the highest-voltage tap Tl3. This auxiliary control-circuit 52 also contains three serially connected contacts; namely a C13 back-contact 51, which is closed when the tap-switch C13 is open; an'XT make-contact '58, which is closed when the auxiliary transition-relay XT is energized; and a C12 make-contact 59, which is closed if the tap-switch CH2, which is being controlled by the circuit 52, is already closed when the auxiliary transition-relay XT is energized. The operation of the auxiliary control-circuit 52 is effective during the retrogressive movement of the master-controller, from the position 15 to the position 14, and will 'be readily understood from the previously given explanation of the operation of the other circuit 51, this retrogressive operation being indicated by the sequence-chart in Fig. 3.

As previous1y intimated in connection with the prevention of backstair circuits and the rectifiers 43, our invention is applicable to multipleunit control, in which two or more identical equipments (similar to the one illustrated) are controlled from one master-controller MC. In such cases, our auxiliary control-circuits 5| and 52 are advantageous in making the transitionsequences, either up or down, of each unit or railway-car, dependent upon the operating speeds and the operational conditions of its own switches, independently of the conditions existing in any other unit or vehicle of the train, and also independently of the speed of movement of a controller-drum or any other outside action. In other words, our auxiliary control-circuits 5| and 52 permit the transition-producing switches to operate at whatever speeds they will, either fast or slow, and the successive steps of the transition will be made when the switches are ready for them, and at no other time.

After the master-controller MC has reached its position 15, in the process of the motor-acceleration, the motor can be still further accelerated by notching the master-controller further forward, to positions 16 and 1? respectively, during which time the voltage is again stepped up, one step at a time, in the same. man ner which was described for the original voltageincreasing steps 13 and 14 of the master-controller.

So far, we have specifically described our invention without reference to the nature of the traction-motor A, other than to say that it is essentially a series commutator-type motor, having a series main-field winding 29 which is adapted to be shunted by a field-shunt 34 for a short-field operation of the motor. Our invention is generally applicable to any traction-motor answering this broad description, and operating on variable-voltage taps of a single-phase main transformer 23.

Our present invention was particularly designed, however, for a rectifier-powered locomotive, such as is shown in the Hibbard application Serial No. 232,811, filed June 21, 1951; also a Hibbard application Serial No. 120,331, filed October 8, 1949; and also a Hibbard application Serial No. 210,390, filed February 10, 1951.

Thus, our invention is illustrated as being applied to a rectifier-powered locomotive in which the traction motor A is a direct-current motor, and in which the transformer secondary-winding 24 has its mid-point X connected to the one terminal of the motor, and said transformer secondary-winding also has asecond group of variable-voltage taps TI to T13, disposed on the opposite side of the mid-tap X, opposite from the side containing the previously described voltage- 9 changing taps Ti to T53. In like manner, each of the several contactor-swltches Ci to CH5 has two correspondingly numbered main-circuit contacts CI to CM, so as to provide a second group 66 of tap-switch contacts Ci to Old which are connected between the second group of transformer-taps Ti to Tit and a second preventive coil PC, the latter having a mid-tap preventivecoil lead 2? which also serves to energize the motor A from the main transformer 23.

The series direct-current motor A is energized, from the two mid-tap preventive-coil leads 21 and 27, through rectifiers (il and El, respectively, through a pair of mutually coupled anode-lead reactors B8. The anode-leads of the rectifiers Bi and B7 are also preferably shunted by an alternating-current filter 69, as previously described in connection with the rectifier-powered locomotive and the previously mentioned applications thereon.

While we have shown and mentioned only one traction-motor, namely the motor having the armature A, and while we have otherwise described our invention in an extremely simplified form, and in only one illustrative application or form of embodiment, we wish it to be understood that our invention is susceptible of many variations, including the use of a plurality of motors, the substitution of various equivalents, the omission or addition of various features or parts or additional safeguards, and other changes which will suggest themselves to the skilled workers of the art, as difierent situations arise.

We claim as our invention:

1. Control-equipment including the combination, with (a) a main single-phase transformer having a plurality of voltage-changing taps at successive points along at least one portion of a winding thereof, (aa) a plurality of tap-switches for changing said taps in a plurality of successsive stages, (ab) a mid-tapped preventive autotransformer-coil having one of its terminals connected to alternate tap-switches, and having its other terminal connected to the remaining tap-switches, (ac) a motor energized from the main transformer and including a motorenergizing mid-tap preventive-coil lead which is connected to the mid-tap of the preventive coil,

of (b) a multi-step voltage-increasing motorpreventive coil are energized; and in successive steps, in the voltage-increasing order of progression, increased voltages are applied, first to one terminal and then to the other terminal of the preventive coil, the transitions between successive steps being accomplished by first causing an opening of the tap-switch which has been energizing the preventive-coil terminal whose voltage is to be increased, and then immediately causing a closure of the tap-switch which applies the increased voltage to that terminal of the preventive coil, meanwhile maintaining an uninterrupted power-supply to the other terminal of said preventive coil during said transition, whereby the voltage on said mid-tap preventivecoil lead is progressively increased, in sequential steps, to a predetermined maximum-voltage value, without any interruption in the powersupply, and (ha) a reduced-voltage motorswitching means, including control-means for actuating the same after a completion of the operation of the multi-step voltage-increasing motor-accelerating means (13) in the motor-am celerating procedure of operation, said reducedvoltage motor-switching means including a means for making a change in the motor-operating connections, and also including a means for etlecting a retrogressive sequential closing of the tap-switches in pairs, to achieve a reduced voltage which is at least two steps below the predetermined maximum voltage of the rnulti-step voltage-increasing motor-accelerating means (31), said retrogressive sequential tap-switch closing being a reversal of a portion of the voltage-increasing procedure described for said multi-step voltage-increasing motor-accelerating means (b).

2. The invention as defined in claim 1, in combination with (bb) a plural-stepped second voltage-increasing motor-accelerating means, for sequentially increasing the voltage from said reduced-voltage value to a predetermined maximum-voltage value, in the motor-accelerating order of progression, in the manner prescribed for the multi-step vcltage-increasing motor-accelerating means (1)), said plural-stepped second voltage-increasing motor-accelerating means (122]) including control-means for actuating the same after a completion of the operation of the reduced-voltage motor-switching means (ha) in the motor-accelerating procedure of operation.

3. Control-equipment including the combination, with (a) a main single-phase transformer having a plurality of voltage-changing taps at successive points along at least one portion of a winding thereof, (cm) a plurality of separate, electrically controlled tap-switches for changing said taps in a plurality of successive stages, (ab) a mid-tapped preventive autotransformer coil having one of its terminals connected to alter nate tap-switches, and having its other terminal connected to the remaining tap'switches, (ac) interlocking means associated with each of the tap-switches for opening that tap-switch in response to an open condition of the next adjacent lower-voltage tap-switch on the same terminal of the preventive coil, and (ad) a motor energized from the main transformer and including a motor-energizing mid-tap preventive-coil lead which is connected to the mid-tap of the preventive coil, of (b) a multi-step motor-com trolling means, including a separate controlcontact for each tap-switch, and a multi step voltage-changing control-portion for sequentially closing successive control-contacts in pairs, so that, at each runningstep of said voltagechanging control-portion, both terminals of the preventive coil are energized; and in successive steps, in the voltage-increasing order of progression, increased voltages are applied, first to one terminal and then to the other terminal of the preventive coil, the transitions between successive steps being accomplished by opening the control-contact for the tap-switch which has been energizing the preventive-coil terminal whose voitage is to be increased, and closing the control contact for the tap-switch which applies the increased voltage to that terminal of the preventive coil, meanwhile maintaining an uninterrupted power-supply to the other terminal of said preventive coil during said transition, where by the voltage on said mid-tap preventive-coil lead is progressively increased, in sequential steps, to a predetermined maximum-voltage value, without any interruption in the powersupply, (bu) said motor-controlling means also including a reduced voltase motor-switching step, next following said predetermined maximum-voltage step in the motor-accelerating order of progression, said motor-switching step including a means for making a change in the motor-operating connections, and also including a means for effecting an opening of the controlcontacts for the maximum-voltage tap-switches for both of the terminals of the preventive coil, and a closure of the control-contacts for two lower-voltage tap-switches, one for each terminal of the preventive coil, and (c) a means for providing an auxiliary control-circuit around the control-contacts for at least a high-voltage one of the tap-switches which are affected by the transition from said maximum-voltage step to said reduced-voltage motor-switching step, said auxiliary control-circuit roviding automatic interlocking-means whereby the voltage-decrease is made progressively, without power-interruption, said auxiliary control-circuit including a contact-means which remains closed until the closure of a decreased-voltage tap-switch which is connected to the preventive-coil terminal opposite to the terminal which is fed by the tapswitch under the control of said auxiliary control-circuit.

4. The invention as defined in claim 3, in which (bb) said motor-controlling means further includes a plural-stepped second voltage-changing control-means, next following the reduced-voltage motor-switching step in the motor-accelerating order of progression, for sequentially increasing the voltage from said reduced-voltage value to a predetermined maximum-voltage value, in the motor-accelerating order of progression, in the manner prescribed for the multi-step voltagechanging control-portion (b).

5. The invention as defined in claim 3, characterized by said auxiliary control-circuit (c) serially including a circuit-making means which is closed both when the multi-step voltagechanging control-portion (b) is on its maximumvoltage step and when the motor-controlling means is on its reduced-voltage motor-switching step (be), another circuit-making means which is closed when said one of the tap-switches is closed, and a circuit-breaking means which is opened when one of the next lower-voltage tapswitches is closed.

6. The invention as defined in claim 5, characterized by the two lower-voltage tap-switches of the reduced-voltage motor-switching step (be) being of a voltage which is next lower than the maximum voltage step of the multi-step voltagechanging control-portion (b).

'7. Control-equipment including the combination, with (a) a main single-phase transformer having a plurality of voltage-changing taps at successive points along at least one portion of a winding thereof, (aa) a plurality of separate, electrically controlled tap-switches for changing said taps in a plurality of successive stages, (ab) a mid-tapped preventive autotransformer-coil having one of its terminals connected to alternate tap-switches, and having its other terminal connected to the remaining tap-switches, (ac) interlocking means associated with each of the tapswitches for opening that tap-switch in response to an open condition of either one of the next adjacent higher and lower-voltage tap-switches on the same terminal of the preventive coil, and (ad) a motor energised from the main transformer and including a motor-energizing mid-tap preventive-coil lead which is connected to the mid-tap of the preventive coil, of (b) a multistep motor-controlling means, including a separate control-contact for each tap-switch, and a multi-step voltage-changing control-portion for sequentially closing successive control-contacts in pairs, so that, at each running-step of said voltage-changing control-portion, both terminals of the preventive coil are energized; and in successive steps, in either a voltage-increasing or a voltage-decreasing order of progression, altered voltages are applied, first to one terminal and then to the other terminal of the preventive coil, the transitions between successive steps being accomplished by opening the control-contact for the tap-sivitch which has been energizing the preventive-coil terminal whose voltage is to be changed, and closing the control-contact for the tap-switch which applies the altered voltage to that terminal of the preventive coil, meanwhile maintaining an uninterrupted power supply to the other terminal of said preventive coil during said transition, whereby the voltage on said midtap preventive-coil lead is progressively changed, in sequential steps, between the limits of a predetermined minimum-voltage value and a predetermined maximum-voltage value, without any interruption in the power-supply, (be) said motor-controlling means also including a reduced-voltage motor-switching step, next following said predetermined maximum-voltage step in the motor-accelerating order of progression, said motor-switching step including a means for making a change in the motor-operating connections, and also including a means for effecting an opening of the control-contacts for the maximumvoltage tap-switches for both of the terminals of the preventive coil, and a closure of the controlcontacts for two lower-voltage tap-switches, one for each terminal of the preventive coil, and (c) a means for providing a separate auxiliary control-circuit around the control-contacts for each of a plurality of the tap-switches which are airected by the transition from said maximumvoltage step to said reduced-voltage motor-- switching step, and vice versa, said auxiliary control-circuits providing automatic interlockingmeans whereby the voltage-change is made progressively, without power-interruption, each auxiliary control-circuit including a contact-means which remains closed until the closure of a changed-voltage tap-switch which is connected to the preventive-coil terminal opposite to the terminal which is fed by the tap-switch under the control of said auxiliary control-circuit.

3. The invention as defined in claim 7,'in which (bb) said motor-controlling means further includes a plural-stepped second voltage-changing control-means, next following the reduced-voltage motor-switching step in the motor-accelerating order of progression, for sequentially increasing the voltage from said reduced-voltagevalue to a predetermined maximum-voltage value, in the motor-accelerating order of progression, in the manner prescribed for the multistep voltage-changing control-portion (b) 9. The invention as defined in claim 7, characterized by at least one of. said auxiliary controlcircuits (0) serially including a circuit-making means which is closed both when the multi-step voltage-changing control-portion (b) is on its maximum-voltage step and when the motor-controlling means is on its reduced-voltage motorswitching step (ba), another circuit-making means which is closed when one of the highestvoltage tap-switches of the multi-step voltagechanging control-portion (b) is closed, and a ciredit-breaking means which is opened when the next lower-voltage tap-switch on the other terminal of the preventive-coil is closed; and further characterized by at least another one of said auxiliary control-circuits (c) serially including a circuit-making means which is closed both when the multi-step voltage-changing control-portion (b) is on its maximum-voltage step and when the motor-controlling means is on its reducedvoltage motor-switching step (ba), another circuit-making means which is closed when one of said lower-voltage tap-switches of the reducedvoltage motor-switching step (ha) is closed, and a circuit-breaking means which is opened when the next higher-voltage tap-switch on the other terminal of the preventive-coil is closed.

10. The invention as defined in claim 9, characterized by the two lower-voltage tap-switches of the reduced-voltage motor-switching step (ha) being of a voltage which is next lower than the maximum voltage step of the multi-step voltagechanging control-portion (b).

11. Control-equipment including: (a) a main single-phase transformer having a plurality of voltage-changing taps at successive points along at least one portion or" a winding thereof, (b) a pair of tap-switches connected to each of said voltage-changing taps oi the main transformer, (c) a mid-tapped preventive autotransformercoil having each of its terminals connected to one of the two tap-switches for each of said voltage-changing taps, (d) a series commutatortype motor having an armature and a series exciting-field winding connected to be energized from the main transformer and including a motor-energizing mid-tap preventive-coil lead which is connected to the mid-tap of the preventive coil, (e) a field-shunting means for said motor, including a field-shunt switching-means for connecting a field-shunting impedance across the series exciting-field winding, (f) a multistep voltage-increasing motor-accelerating means, for causing the sequential closing of said tap-switches in pairs, so that, at each running-- step of said voltage-increasing motor-accelerating means, both terminals of the preventive coil are energized; and in successive steps, in the voltage-increasing order of progression, increased voltages are applied, first to one terminal and then to the other terminal of the preventive coil, the transitions between successive steps being accomplished by first causing an opening of the tapswitch which has been energizing the preventivecoil terminal whose voltage is to be increased, and then immediately causing a closure of the tap-switch which applies the increased voltage to that terminal of the preventive coil, meanwhile maintaining an uninterrupted power-supply to the other terminal of said preventive coil during said transition, whereby the voltage on said mid-tap preventive-coil lead is progressively increased, in sequential steps, to a predetermined maximum-voltage value, without any interruption in the power-supply, and (g) a reduced voltage-field-shunting means, including controlmeans for actuating the same after a completion of the operation of the multi-step voltage-increasing motor-accelerating means (,T') in the motor-accelerating procedure of operation, said reduced-voltage field-shunting means including a means for effecting a field-shunting actuation of said field-shunting switching-means (c), and also including means for effecting a retrogressive sequential closing of the tap-switches in pairs, to achieve a reduced voltage which is at least two steps below the predetermined maxi- 14 mum Voltage of the multi-step voltage-increasing motor-accelerating means (f), said retrogressive sequential tap-switch closing being a reversal of a portion of the voltage-increasing procedure described for said multi-step voltageincreasing motor-acce1erating means (i).

12. The invention as defined in claim 11, in combination with (h) a plural-stepped second voltage-increasing motor-accelerating means, for sequentially increasing the voltage from said reduced-voltage value to a predetermined maximum voltage value, in the motor-accelerating order of progression, in the manner prescribed for the multi-step voltage-increasing motoraccelerating means (f), said plural-stepped second voltage-increasing motor-accelerating means (h) including control-means for actuating the same after a completion of the operation of the reduced-voltage field-shunting means (9') in the motor-accelerating procedure of operation.

13. Control-equipment including: (a) a main single-phase transformer having a plurality of voltage-changing taps at successive points along at least one portion of a Winding thereof, ('b) a pair of separate, electrically controlled tapswitches connected to each of said voltage-changing taps of the main transformer, (c) a midtapped preventive autotransformer-coil having each of its terminals connected to one of the two tap-switches for each of said voltage-changing taps, (d) interlocking means associated with each of the tap-switches for opening that tap-switch in response to an open condition of the next adjacent lower-voltage tap-switch on the same terminal of the preventive coil, (6) a series commutator-type motor having an armature and a series exciting-field winding connected to be energised from the main transformer and including a motor-energizing mid-tap preventivecoil lead which is connected to the mid-tap or" the preventive coil, (f) a field-shunting means for said motor, including a field-shunt switchingmeans for connecting a field-shunting impedance across the series exciting-field winding, (g) a multi-step motor-controlling means, including a separate control-contact for each tap-switch, and a multi-step voltage-changing control-portion for sequentially closing successive controlcontacts in pairs, so that, at each running-step of said voltage-changing control-portion, both terminals of the preventive coil are energized; and in successive steps, in the voltage-increasing order of progression, increased voltages are applied, first to one terminal and then to the other terminal of the preventive coil, the transitions between successive steps being accomplished by opening the control-contact for the tap-switch which has been energizing the preventive-coil terminal whose voltage is to be increased, and closing the control-contact for the tap-switch which applies the increased voltage to that terminal of the preventive coil, mean-- while maintaining an uninterrupted power-suppiy to the other terminal of said preventive coil during said transition, whereby the voltage on said mid-tap preventive-coil lead is progressively increased, in sequential steps, to a predetermined maximum-voltage value in which the two highest-voltage tap-switches are closed, without any interruption in the power-supply, (ya) said motor-controlling means also including a reduced-voltage field-shunting step, next following said predetermined maximum-voltage step in the motor-accelerating order of progression, said field-shunting step including a means for efiecting a field-shunting actuation of said field-shunting switching-means (f), and also including a means for effecting an opening of the controlcontacts for the maximum-voltage tap-switches for both of the terminals of the preventive coil, and a closure of the control-contacts for the two next-adjacent lower-voltage tap-switches, and (it) a means for providing an auxiliary controlcircuit around the control-contact for one of the two highest-voltage tap-switches, said auxiliary control-circuit providing automatic interlockingmeans whereby the voltage-decrease is made progressively, without power-interruption, said auxiliary control-circuit including a contactmeans which remains closed until the closure of the next-adjacent lower-voltage tap-switch which is connected to the other terminal of the preventive coil.

14. The invention as defined in claim 13, in which (gb) said motor-controlling means further includes a plural-stepped second voltagechanging control-means, next following the reduced-voltage field-shunting step in the motoraccelerating order of progression, for sequentially increasing the voltage from said reduced-voltage value to a predetermined maximum-voltage value, in the motor-accelerating order of progression, in the manner prescribed for the multistep voltage-changing control-portion (g).

15. The invention as defined in claim 13, characterized by said auxiliary control circuit (h) serially including a circuit-making means which is closed both when the inulti-step voltagechanging control-portion (g) is on its maximumvoltage step and when the motor-controlling means is on its reduced-voltage field-shunting step (ga), another circuit-making means which is closed when said one of the tap-switches is closed, and a circuit-breaking means which is opened when one or" the next lower-voltage tapswitches is closed.

16. Control-equipment including; (a) a main single-phase transformer having a plurality of voltage-changing taps at successive points along at least one portion of a winding thereof, ('0) a pair of separate, electrically controlled tap switches connected to each of said voltagechanging taps oi the main transformer, (c) a mid-tapped preventive autotransiormer-coil having each of its terminals connected to one of the two tap-switches for each or said voltage-changing taps, (d) interlocking means associated with each of the tap-switches for opening that tapswitch in response to an open condition or either one of the next adjacent higher and lower-voltage tap-switches on the same terminal of the preventive coil, re) a series commutator-type motor having an armature and a series exciting-field winding connected to be energized from the main transformer and including a motor-energizing mid-tap preventive-coil lead which is connected to the mid-tap of the preventive coil, (1) a fieldshunting means for said motor, including a fieldshunt switching-means for connecting a fieldshunting impedance across the series excitingfield winding, (9) a niulti-step motor-controlling means, including a separate control-contact for each tap-switch, and a multi-step voltage-changing control-portion for sequentially closing successive control-contacts in pairs, so that, at each running-step of said voltage-changing controlportion, both terminals of the preventive 0011 are energized; and in successive steps, in either a voltage-increasing or a voltage-decreasing order of progression, altered voltages are applied, first to one terminal and then to the other terminal of the preventive coil, the transitions between successive steps being accomplished by opening the control-contact for the tap-switch which has been energizing the preventive-coil terminal whose voltage is to be changed, and closing the controlcontact for the tap-switch which applies the altered voltage to that terminal of the preventive coil, meanwhile maintaining an uninterrupted power-supply to the other terminal of said preventive coil during said transition, whereby the voltage on said mid-tap preventive-coll lead is progressively changed, in sequential steps, between the limits or a predetermined minimum-voltage value and a predetermined maximum-voltage value in which the two highest-value tap-switches are closed, without any interruption in the powersupply, (go) said motor-controlling means also inculding a reduced-voltage field-shunting step, next following said predetermined maximumvoltage step in the motor-accelerating order of progression, said field-shunting step including a means for eflecting a field-shunting actuation of said field-shunting switching-means (j), and also including a means for effecting an opening of the control-contacts for the maximum-voltage tapswitches for both of the terminals of the preventive coil, and a closure of the control-contacts for the two next-adjacent lower-voltage tapswitches, and (it) a means for providing a sepa rate auxiliary control-circuit around the respective control-contacts for one of the two highestvoltage tap-switches and for the next-adjacent lower-voltage tap-switch which is connected to the other terminal of the preventive coil, respectively, said auxiliary control-circuits providing automatic interlocking-means whereby the voltage-change is made progressively, without powerinterruption, each auxiliary control-circuit including a contact-means which remains closed until the closure of the tap-switch which is controlled by the other auxiliary control-circuit.

17. The invention as defined in claim 16, in which (gb) said motor-controlling means further includes a plural-stepped second voltage-v changing control-means, next following the re duced-voltage field-shunting step in the motoraccelerating order of progression, for sequentially increasing the voltage from said reduced-voltage value to a predetermined maximum-voltage value, in the motor-accelerating order or progression, in the manner prescribed for the multi-step voltagechanging control-portion (g).

18. The invention as defined in claim 16, characterized by each of said auxiliary control-circuits (it) serially including a circuit-making means which is closed both when the multi-step voltage-changing control-portion (g) is on its maximum-voltage step and when the motor-controlling means is on its reduced-voltage fieldshunting step (get), another circuit-making means which is closed when its own tap-switch is closed, and a circuit-breaking means which is opened when the tap-switch which is controlled by the other auxiliary control-circuit is closed.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,632,873 Hibbard Mar. 24, 1953 

